It is not possible to employ a method of channel coding for supressing the DC component of a signal, when high frequency data such as a digital video signal is to be recorded, because the margin of carrier to noise ratio (C/N) decreases.
For example, it is not possible to use a channel coding which increases the bit rate, such as a 8-10 conversion which converts 8 bits data to 10 bits data. A method of channel coding which has a density ratio (a ratio of minimum distance of reverse magnetization before modulation and after modulation) more than 1 has been suggested, but for 2-7 conversion, for example, it is difficult to make an integrated circuit because the frequency of the master clock is doubled.
An ME tape is suitable for high density recording, but it has the characteristic of lacking capability of recording and reproducing low frequency components (i.e., a low frequency lacking effect).
Moreover, it is difficult to transmit a DC component when a rotary head and a rotary transformer is used. As mentioned above, the low frequency components of transmitted data are lost. For compensating for a lost low frequency component, a phase equalizer was needed in a prior art integral-detection method.
However, it is not easy to adjust a phase equalizer for proper matching.